All mammals include a variety of channels for moving fluids or materials from one location within the body to another. In general these channels are called tubes, ducts, foramina, cavities, canals and vessels some of which have internal flow controls i.e., sphincters, capillary bed, etc. Specifically these channels include fallopian tubes, naso-lacrimal ducts, blood vessels, vas deferens, cavities within the bone and the like. Unless these channels are diseased, surgically altered or damaged in some manner, they continue to provide a means for conducting fluid or material through them for at least part of the time. If they are surgically altered, it may become important to secure a prosthetic element in place. Such channels may be voluntarily closed by the mammal such as by muscular movements or contractions. However, they all remain open part of the time. There are certain advantages to overriding the natural physiology for a sustained period of time and completely closing off particular channels in order to obtain particular desirable results. Depending on the particular channel to be closed, a number of different procedures have been developed in order to temporarily or permanently close such channels, with or without securing prosthesis in place. Some of these procedures are described below.
Blocking the Canaliculus
Mammalian eyes include a complex composition in the form of a tear film. Tears include three basic component layers comprising (1)lipids, (2)an aqueous layer, and (3)mucin. The absence of any one of the layer components causes discomfort and can lead to temporary or permanent dry eye syndromes (SICCA). Each of the component layers has a particular function. The lipid layer prevents evaporation of the tears from the surface of the eye. The aqueous layer is the major component of the tears, and is responsible for providing oxygen to the cornea and contains a number of additional chemical components which are important to a healthy eye. The mucin material provides for interaction between the lipid layer and the aqueous layer and keeps the tears from beading up on the cornea, which will occur in the absence of mucin.
The importance of a tear layer on a healthy mammalian eye can be generally understood based on the above explanation. However, from time to time the eye suffers from a lack of tears (dry eye), which can have a variety of causes but is generally attributed to one or two basic malfunctions. First, the tear ducts leading from the lacrimal glands can be clogged or malfunctioning so that insufficient amounts of tears reach the eye. This was generally thought to be the main reason for dry eye for a considerable period of time. In response, artificial tears were developed and administered to eyes. The relief enjoyed by these tears are short-lived and must be readministered several times each hour. More recently, it has been noted that most tear producing glands can deliver sufficient amounts of tears to the eye, but that the tears are drained away from the eye too quickly, thereby creating a dry eye situation. Accordingly, recent therapies have proceeded on the basis that tear production is adequate in most individuals, and that a significant percentage of dry eye syndrome is caused by excessive tear removal.
Tears are removed from the eye by draining first through upper and lower punctal openings which lead into the canalicular canals. Initial attempts at sealing the puncta and/or the canalicular canals involved stitching the puncta shut or using electrical or laser cauterization to seal the puncta and or canalicular canals. Although such methodology can provide desirable results, the procedure is not reversible without reconstructive surgery. Since it is sometimes difficult to determine whether the drainage is too great or the tear production is too small, irreversible blockage is a condition which is not without risk. If tear production is completely eliminated, it will not solve the problem and the patient would have been exposed to unnecessary expense and trauma. Alternatively, it can result in a situation where normal tear flow is restored and tears continually form on the eye, build up and pour onto the face of the patient. (epiphera).
In order to provide for an autoreversible technique for sealing the puncta or canalicular canals, collagen implants were developed. These implants were designed to be water soluble and were placed in the puncta and/or canalicular canals in order to provide for a test procedure on the patient. Over a period of seven to fourteen days, the implants dissolved. The patient was observed over this time, and it was determined whether it would be desirable to permanently seal the puncta.
Water-insoluble plugs which can be placed in the punctum openings and into vertical sections of the canalicular canals are disclosed within U.S. Pat. No. 3,949,750 to Freeman. Although these plugs are reversible, they tended to become dislodged quite easily. Further, they are somewhat difficult to insert, and occasionally their size and shape can cause tissue damage during insertion or, if they protrude from the puncta, they can cause irritation to the sclera. The tissue of the punctum can also be damaged by being dilated by the plugs over long periods of time.
An improvement on the Freeman plugs is disclosed within U.S. Pat. 4,959,048 to Seder et al., issued Sep. 25, 1990. Seder et al. disclose a preformed plug or channel occluder which is somewhat conical in shape, making it possible to insert the occluder into the opening of the punctum more easily than the devices disclosed by Freeman. Further, Seder et al. disclose that variations in the anatomy of individuals make it desirable to provide a series of occluders which are provided in different lengths and/or widths in order to accommodate the anatomical differences. Further, the surface of the plugs may be coated with a lubricant.
Occluding Reproductive Channels
The mature sperm of mammals moves through excretory channels of the testes which are referred to as the vas deferens. A well-known means of male contraception is achieved by carrying out a procedure referred to as a vasectomy, wherein the vas deferens are severed or sealed surgically. Once the channel has been severed, it is difficult to reconnect channels so that they can function properly. In order to attempt to provide some degree of reversibility with respect to this procedure, mechanical valves have been developed and inserted into the vas deferens in a manner which interrupts the flow of sperm through the duct channel. Although this procedure provides a degree of reversibility in that the valves can be opened or closed, the procedure is not without difficulties. First, it is extremely difficult to produce such small valves and to insert them within small channels in a manner which does not damage the channels while making sure that the valves can later be reopened and allow the channels to operate normally. Further, the seal created by such valves is sometimes not complete. Maintaining a healthy, viable seal between living tissue and an inert organic prosthetic device is difficult to accomplish when the device is not designed to conform precisely to the size and shape of the duct channel.
Methods of rendering female mammals infertile include tying ligatures around the fallopian tubes. Thermosetting silicones have been used to fill these tubes to render women infertile. Alternatively, the surfaces of the tubes may be chemically or thermally scarred in such a manner that after healing, the duct channel is closed, preventing the movement of eggs through the channel. In order to reverse such procedures, it is necessary to attempt to remove the damaged portion of the duct channel and surgically connect undamaged ends in a manner so as to provide for a healthy, functionally operating channel. Although a high degree of success is obtained with respect to sealing fallopian tubes, the degree of success with respect to reversing the operation is relatively low.
Closing Off a Blood Supply
In the case where a patient has developed a tumor in an organ, that is inaccessible or the organ is of a nature or in a position that prevents a surgical approach, a method to rid the host of the problem may be to cut off the blood supply and starve the unwanted growth. Rapidly polymerizing monomers such as methyl .alpha.-cyanoacrylate can be deposited in the appropriate vessel by means of an appropriately guided cannula or catheter. When the end of the catheter is in the proper position, the monomer is released. Once exposed to the multitudinous supply of nucleophilic natural agents, the monomer polymerizes and effects blockage. However, the monomer itself is toxic and causes acute inflammation and necrosis to the surrounding tissues. The trauma itself enlists a reaction which causes vascularization to the area and soon the tumor is once again well nourished. In the case where a patient has developed an uncontrolled hemorrhage in, perhaps, the brain, there is too much risk to attempt surgical intervention. The safest way to arrive at the site of hemorrhage is again by a fine guided catheter. A rapidly polymerizing monomer such as methyl a-cyanoacrylate can be deposited in the appropriate vessel at the site of hemorrhage. While the polymerizing monomer is effective in shutting down the blood flow through the broken vessel, it sometimes causes the tip of the catheter to become cemented in place.
Correction of Vascular Abnormalities
A condition known as arteriovenous anastomosis (the joining of an artery and a vein) is a serious problem because anastomosis bypasses the intended capillary bed thus starving the cells fed by that system. Once recognized, the surgeon will attempt appropriate measures to correct the condition. Closing off that abnormality by surgery is direct if the area can be accessed. Usually guided catheterization is used when the identified anastomosis is remote or in accessible. Gelling agents are used but they are normally difficult to repair because of the high flow rate through the abnormality. A quick set time creating a permanent plug is very attractive. A cyanoacrylate can be deposited in the appropriate vessel at the site but the method suffers from the risks as described above.
Closing up a Temporary Channel Made for a Cranial Tap
Not all channels need to be provided to the mammalian body by nature. Some could be man-made channels for example, a temporary cranial tap to permit the release of pooled blood between the brain and the skull after a concussion. After the pressure is reduced, the hole must be sealed to prevent the passage of other fluids or bacteria getting into the brain. A plastic shield may be placed over the channel before the skin is pulled over it and sown closed.
Fastening a pin in the lumen of a bone
Broken bones are frequently supported by steel pins placed within the natural lumen of a finger or limb bone. Hip joint replacements usually require that a new ball fitting be placed at the end of the femur by means of a pin or spike. This spike enters the lumen of the femur. In either case, if the fit is not tight, cement or mastic is used to fill in the space between the pin and the bone to keep the pin in position and prohibit it from moving within the lumen.
The above is not, and is not intended to be, an extensive discussion of all of the different types of channels present within living mammals. Further, the above is not, and is not intended to be, a discussion of all the different types of techniques and procedures and devices which can be used to seal such channels in order to obtain results which may be permanently or temporarily desirable. The above merely provides some limited background information on six particular types of channels found in living mammals, which channels are occluded or sealed by medical procedures and/or devices. Further, the above indicates that by carrying out these procedures and/or using these devices, results which are seen as desirable can be obtained. The present inventor endeavors to provide new techniques and devices for sealing channels within mammals which provide a number of advantages.
While the subject of body temperature is a complex one, (see Body Temperature Regulation, Medical Physiology, eleventh edition Philip Bard Ed., C. V. Mosby 1961.), several features should be called out. First, the average core temperature of humans is not a very consistent number. It varies for individuals over a range of 36.degree. C. to 38.degree. C. However, normal healthy men or women after vigorous exercise can raise their temperature to as high as 42.degree. C. In the morning when the external surroundings are cool, the body temperature can drop to below 33.degree. C. Extremities such as feet can achieve temperatures of 27.degree. C. when the surroundings are cool.
Second, the temperature at which denaturation of cells occurs varies with the section of the body involved and the time over which the cells are exposed to that heat. The brain is perhaps the most sensitive organ. Brain lesions and heat stroke occur in the range of 42.degree. C. to 44.degree. C. Bones can withstand the exotherm created by polymerizing methylmethacrylate which may exceed 60.degree. C. Most cells can withstand 45.degree. C. temperatures for several minutes without any harmful effects as well as they can tolerate 50.degree. C. for several seconds.
With this background the inventor now can reveal the basis of this disclosure.